[sequencemanager] Remove OnTaskReadyHandler support.

TaskQueueImpl supported registering a callback that is invoked when
a task becomes ready. This was only used by the obsolete agent
interference histogram. Therefore, this CL removes support for this
callback.

Bug: 1019856, 984057
Change-Id: I838b88e13174eff5347de55646d22565b770339c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2297719
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788697}

base/task/sequence_manager/sequence_manager_impl_unittest.cc

@@ -4917,23 +4917,6 @@ TEST_P(SequenceManagerTest,
             queue->GetEnqueueOrderAtWhichWeBecameUnblocked());
 }
 
-TEST_P(SequenceManagerTest, OnTaskReady) {
-  auto queue = CreateTaskQueue();
-  int task_ready_count = 0;
-
-  queue->GetTaskQueueImpl()->SetOnTaskReadyHandler(
-      BindLambdaForTesting([&](const Task&, LazyNow*) { ++task_ready_count; }));
-
-  EXPECT_EQ(0, task_ready_count);
-  queue->task_runner()->PostTask(FROM_HERE, DoNothing());
-  EXPECT_EQ(1, task_ready_count);
-  queue->task_runner()->PostDelayedTask(FROM_HERE, DoNothing(),
-                                        base::TimeDelta::FromHours(1));
-  EXPECT_EQ(1, task_ready_count);
-  FastForwardBy(base::TimeDelta::FromHours(1));
-  EXPECT_EQ(2, task_ready_count);
-}
-
 namespace {
 
 class TaskObserverExpectingNoDelayedRunTime : public TaskObserver {

base/task/sequence_manager/task_queue_impl.cc

@@ -297,11 +297,6 @@ void TaskQueueImpl::PostImmediateTaskImpl(PostedTask task,
     any_thread_.immediate_incoming_queue.push_back(Task(
         std::move(task), delayed_run_time, sequence_number, sequence_number));
 
-    if (any_thread_.on_task_ready_handler) {
-      any_thread_.on_task_ready_handler.Run(
-          any_thread_.immediate_incoming_queue.back(), &lazy_now);
-    }
-
 #if DCHECK_IS_ON()
     any_thread_.immediate_incoming_queue.back().cross_thread_ =
         (current_thread == TaskQueueImpl::CurrentThread::kNotMainThread);
@@ -584,9 +579,6 @@ void TaskQueueImpl::MoveReadyDelayedTasksToWorkQueue(LazyNow* lazy_now) {
     DCHECK(!task->enqueue_order_set());
     task->set_enqueue_order(sequence_manager_->GetNextSequenceNumber());
 
-    if (main_thread_only().on_task_ready_handler)
-      main_thread_only().on_task_ready_handler.Run(*task, lazy_now);
-
     delayed_work_queue_task_pusher.Push(task);
     main_thread_only().delayed_incoming_queue.pop();
   }
@@ -1157,16 +1149,6 @@ bool TaskQueueImpl::HasPendingImmediateWorkLocked() {
          !any_thread_.immediate_incoming_queue.empty();
 }
 
-void TaskQueueImpl::SetOnTaskReadyHandler(
-    TaskQueueImpl::OnTaskReadyHandler handler) {
-  DCHECK(should_notify_observers_ || handler.is_null());
-  main_thread_only().on_task_ready_handler = handler;
-
-  base::internal::CheckedAutoLock lock(any_thread_lock_);
-  DCHECK_NE(!!any_thread_.on_task_ready_handler, !!handler);
-  any_thread_.on_task_ready_handler = std::move(handler);
-}
-
 void TaskQueueImpl::SetOnTaskStartedHandler(
     TaskQueueImpl::OnTaskStartedHandler handler) {
   DCHECK(should_notify_observers_ || handler.is_null());

base/task/sequence_manager/task_queue_impl.h

@@ -91,7 +91,6 @@ class BASE_EXPORT TaskQueueImpl {
   };
 
   using OnNextWakeUpChangedCallback = RepeatingCallback<void(TimeTicks)>;
-  using OnTaskReadyHandler = RepeatingCallback<void(const Task&, LazyNow*)>;
   using OnTaskStartedHandler =
       RepeatingCallback<void(const Task&, const TaskQueue::TaskTiming&)>;
   using OnTaskCompletedHandler =
@@ -202,11 +201,6 @@ class BASE_EXPORT TaskQueueImpl {
   // addition MaybeShrinkQueue is called on all internal queues.
   void ReclaimMemory(TimeTicks now);
 
-  // Registers a handler to invoke when a task posted to this TaskQueueImpl is
-  // ready. For a non-delayed task, this is when the task is posted. For a
-  // delayed task, this is when the delay expires.
-  void SetOnTaskReadyHandler(OnTaskReadyHandler handler);
-
   // Allows wrapping TaskQueue to set a handler to subscribe for notifications
   // about started and completed tasks.
   void SetOnTaskStartedHandler(OnTaskStartedHandler handler);
@@ -381,7 +375,6 @@ class BASE_EXPORT TaskQueueImpl {
     //    EnqueueOrder of any already queued task will compare less than this.
     EnqueueOrder
         enqueue_order_at_which_we_became_unblocked_with_normal_priority;
-    OnTaskReadyHandler on_task_ready_handler;
     OnTaskStartedHandler on_task_started_handler;
     OnTaskCompletedHandler on_task_completed_handler;
     // Last reported wake up, used only in UpdateWakeUp to avoid
@@ -505,8 +498,6 @@ class BASE_EXPORT TaskQueueImpl {
 
     bool unregistered = false;
 
-    OnTaskReadyHandler on_task_ready_handler;
-
 #if DCHECK_IS_ON()
     // A cache of |immediate_work_queue->work_queue_set_index()| which is used
     // to index into